Optical fibre switching assembly

ABSTRACT

An optical guide switching assembly in which steering devices are used to assembly deflect radiation from a transmitting guide to a selected receiving guide. Each of the steering devices includes a collimator for light emerging from the transmitting guide and an actuator to cause relative movement between the collimator and the guide to cause the deflection, or to move the guide and collimator together. The actuator can be piezoelectric and of either a foil type, or a monolithic type, and mechanical leverage can be used to improve deflection. Capacitive sensing means provide positional information for feedback control, preferably in a diagonal switching arrangement.

This invention relates to an optical guide switching assembly and tosteering devices used in the assembly for deflecting radiation from atransmitting guide in order to direct the radiation to a selectedreceiving guide.

One of the major problems facing the invention is to provide rapidswitching with low insertion loss (high coupling efficiency and lowcross talk) for high port counts, whilst evolving a compact design whichcan be readily manufactured. A related problem is to increase theswitching capacity of an optical fibre switching assembly, without theexpense of an increase in physical size. At least preferred embodimentsof the invention have been especially designed to deal with theseproblems.

According to the main aspect of the invention, an optical beam switchingassembly comprises:

-   -   (a) a first set of optical guides spaced from a second set of        optical guides, and    -   (b) respective steering devices for causing deflection of a beam        of optical radiation from a selected transmitting guide in the        first set so that it is received by a selected receiving guide        in the second set;    -   characterised in that each of said devices comprises collimating        means for collimating light from said transmitting guide and        means for moving said collimating means or for causing relative        movement between said collimating means and said transmitting        guide to cause said deflection.

Advantages of the latter arrangement include greater deflection for acomparatively smaller movement (of either the collimating means, or thetransmitting guide) and higher switching speeds due to comparativelylower inertia. For example, in the case where an end portion of opticalfibre is subject to transverse movement to deflect an emergent beam, theend portion has less inertia and a wider deflection is possible athigher speed. This is also beneficial in designing a switching assemblyhaving a high packing density of (e.g.) optical fibres.

The optical guide can be, for example, an optical fibre which conductslaser light, or a waveguide made of silicon or other dielectric materialwhich conducts infrared light. These guides. (for example, opticalfibres), can be arranged in the switching assembly so that emergentbeams of radiation are projected directly across a space, i.e. betweenseparated sets of transmitting and receiving optical fibres.Alternatively, they can be arranged in the same array where beams ofradiation are projected from sets of transmitting optical fibres to areflector, which then reflects the beams back to receiving opticalfibres. (Reference made herein to optical fibres is by way of exampleonly and can be taken to cover other forms of optical guide.)

The steering device can include, for example, a piezo electrictransducer for deflecting an end portion of a transmitting fibre so thatthe radiation (which exits from the fibre) is caused to move in thefocal plane of a collimating lens. Alternatively, the end of thetransmitting fibre can be fixed and a collimating lens can be moved withrespect thereto, so that the focal plane of the lens is moved around theend of the fibre to produce the same effect. Alternatively, the end ofthe transmitting fibre can have a collimating lens either integraltherewith, or attached thereto, so that the fibre and the lens can movetogether to produce the same effect.

Instead of using a piezo electric transducer, electrostatic deflectionmeans can be used either to move a fibre with respect to a fixed lens,or to move a lens with respect to a fixed fibre. For example, thesurface of the end portion of the fibre can be metallised or given someother conductive coating, so that it forms one electrostatic movable“plate” which co-operates with fixed electrostatic “plates” adjacent themovable “plate”.

Where a piezo electric transducer is used to cause movement, it can beof a “foil type”, where fingers of a comb-like array of piezotransducers are attached to actuating members, such as foil strips, forproducing orthogonal displacement of either the optical fibre or thelens system. Such foils and combs can be assembled in a laminar matrix.

Alternatively, the piezo electric transducer can be of a “monolithictype” where each transducer is made of piezo electric material, it has abody with a longitudinal axis, and the body has conductive stripsaligned with said longitudinal axis so as to define respective portionsof the piezo electric transducer which are energised to impartrespective transverse movements in different radial directions. Thisprovides a resultant motion in orthogonal axes. A multiplicity of suchbodies can be assembled in a columnar matrix. The body can have a borealigned with its longitudinal axis in which the fibre is received,whereby bending of the fibre occurs with respect to said longitudinalaxis. Alternatively, the body is attached to the collimating lens whichmoves relative to a fixed fibre.

This “foil type” and “monolithic type” which are described in moredetail below, can be designed to provide greater beam deflection thanprior art arrangements, with less inertia, to achieve more rapidswitching between a greater number of fibres and also to provide ahigher packing density of fibres.

Preferably, position sensing feedback means are employed for sensing theamount of movement and for providing a feedback signal. This is used ina control system which energises the transducers to ensure that thetransmitted radiation is aimed at the correct receiver fibre for makingthe required switching connection.

Preferably, a capacitive feedback system is used. For example, the fibreend has a conductive coating (as one “capacitor plate”) and it moveswith respect to fixed conductive tracks (acting as the other “capacitorplate”). The term “capacitor plate” applies generally to any member,surface, or structure which, together with the intervening “dielectric”(which could be air, a liquid or gaseous fluid, or some other dielectricmaterial), forms a good capacitive coupling between fixed and movingelements. Such “plates” can therefore take various forms, e.g. they canbe flat, curved or parts of some structure having some inherentcapacitive properties. In another example, a lens system or opticalcollimator, having an associated “capacitor plate”, moves with respectto a fixed fibre end, having an associated “capacitor plate”.

In a preferred embodiment of the invention, conductive tracks oninsulating boards are arranged in layers to form one set of fixedcapacitive plates of a position sensing feedback system; the moving endportions of respective fibres having conductive coatings to form theother plates. Alternatively, a conductive plate moves with a lens, andanother conductive plate is fixed with the fibre. These tracks can crossorthogonally so that pairs of conductive tracks, associated withindividual fibres, can be polled or addressed so as to sense the changein capacity proportional to the relative displacement between the fibreends and the lens systems. In a preferred embodiment, a diagonaladdressing system is used which can be selectively energized andswitched in order to detect an instantaneous capacitive value relatingto the amount of beam deflection.

When using the monolithic type of (piezo electric material) transducer,its rod-like form may be comparatively short and thick whereby bendingis limited with respect to the longitudinal axis. In this case,mechanical leverage means can be used so as to magnify the transducermovement before imparting motion to cause relative movement between thecollimating lens and the end portion of the fibre, or to move the endportion of the fibre to which a collimator lens is attached or forms anintegral part. Preferably, such leverage means includes a gimbalmounting and an extension rod located between the end of the body of thepiezo electric material transducer and a point on the gimbal spaced fromits pivotal axis. In the latter case, where the collimator is part of orattached to the fibre end, the gimbal mounting is preferably on the bodyof the collimator to provide optimum deflection of the emergent beam.

Embodiments of the invention will now be described with reference to theaccompanying drawings in which:

FIG. 1 is a schematic cross section through one embodiment of a foiltype of device for moving optical fibres;

FIG. 2 is a similar cross section through a monolithic type;

FIG. 3 is a perspective view showing foil actuating strips (driven bypiezo electric material actuators) supporting fibre optics;

FIG. 4 is an elevational cross section to a foil type sub-assembly;

FIGS. 5 and 6 are different perspective views of a 4-port switchassembly, including 4 lenses, showing piezo combs connected to foilstrips for moving optical fibres in the focal plane of lenses (only 4ports are shown to simplify explanation, since multiplicity of portswould be employed in practice);

FIGS. 7 a-7 d are perspective views showing the stages of manufacture ofa monolithic type of actuator, and FIG. 7 e is a plan view;

FIG. 8 shows a group of monolithic actuators and lenses;

FIG. 9 is a schematic elevation through a monolithic actuator assemblywith a lens array (when a hexagonal array of fibres and actuator isused);

FIG. 10 shows the sub-assembly of FIG. 9 used in a reflective type ofswitching assembly in which radiation is projected through ahalf-silvered mirror onto a CCD;

FIG. 11 shows the sub-assembly of FIG. 9 used in a pass-through type ofswitching assembly in which radiation passes directly from transmitterfibres to receiver fibres and FIGS. 11 a and 11 b are diagrams forfurther explanation;

FIG. 12 is a schematic cross section illustrating a capacitive sensingarrangement;

FIGS. 13 a-13 b show another embodiment of capacitive sensing;

FIG. 14 is a schematic electronic diagram;

FIG. 15 shows a technique of diagonal switching explained in detailbelow;

FIG. 16 shows fibres with attached and integral collimator lens;

FIG. 17 shows collimator arrangements with monolithic types;

FIG. 18 shows a gimbal mounting for a collimator;

FIG. 19 shows an alternative gimbal mounting;

FIG. 20 shows an exaggerated effect of tilting the gimbal mounting andcollimator;

FIG. 21 shows a detail of a foil type connection structure for gimbaland translational mounting of collimators;

FIG. 22 shows an array of piezo tube type actuators on a triangulararray;

FIGS. 23 a and 23 b are side views of an embodiment using a moving lensand a fixed fibre;

FIG. 24 is a isometric view of the latter embodiment using a moving lensand a fixed fibre;

FIG. 25 shows a group of the arrangement of the devices shown in FIG.24;

FIGS. 26 a-26 e shows an example of each of five different foil designsin plan view for a five-layer 64 port foil type switch assembly;

FIG. 27 is a perspective view of a piezo comb actuator; FIG. 27 a showsa detail of the electrical connectors and FIG. 27 b shows connectiondetails for the piezo comb actuator of FIG. 27 a;

FIGS. 28 a-28 e show different plan sectional views of each of 5 layersof piezo comb arrays and foil arrangements;

FIG. 29 shows a sub-assembly (foil type) of a switch (including 64ports), and

FIG. 30 shows a rear view of the switching sub-assembly (foil type);

FIGS. 31 a-31 c are isometric views of a sub-assembly of monolithic typeactuators;

FIGS. 32 and 33 each show other switching assemblies; and

FIG. 34 shows two of the assemblies of FIG. 33 used with spacedtransmitter and receiver fibre sets.

FIG. 1 schematically illustrates “foil type” devices which can be used,for example, for moving optical fibres. In each device, piezo electrictransducer elements 1 a, 1 b; 2 a, 2 b form respective sets of fingersof a comb structure fixed at one end to a support unit 3. The ends ofthe fingers are fixed to respective foils 4 a, 4 b, with pairs ofcomb-like structures located on opposite sides of respective fibres 5 a,5 b. Each fibre, such as fibre 5 a, is fixed to respective foil sets 4a, by a bead of adhesive 6 a or solder contacts if the fibre ismetallised. The piezo electric material transducer elements 1 a, 1 b; 2a, 2 b bend (in parallel) in the same direction so as to impart“push/pull” movement to the respective fibre (in one of two orthogonaldirections). Other piezo electric material transducer elements (notshown and which are arranged perpendicularly to the former elements)bend similarly (but in a different orthogonal direction so as to impart“push/pull” movement to the respective fibre. The resultant provides thefibre with two degrees of motion in orthogonal directions. Accordingly,radiation passing through the fibre 5 a and leaving from the end 5 a′can be deflected anywhere in an x-y plane. The “radiation” can be laserlight, or light from an LED, for example, but it can also be other formsof electromagnetic energy.

FIG. 2 schematically illustrates a “monolithic type”, where each of thepiezo elements 7 a, 7 b has a cylindrical or rod-shaped body with acentral bore along its longitudinal axis in which the optic fibre 5 a, 5b is received. One end of each piezo element 7 a, 7 b is firmly securedto support unit 3, and the free end is free to move as a result ofbending of the body with respect to the longitudinal axis (as explainedbelow). The drawing also shows electrical interconnects 8 a, 8 b to thepiezo elements. As with the foil type, radiation leaving the end 5 a′ isdeflected by bending the fibre 5 a in the x-y plane.

FIG. 3 shows an enlargement of a modified “foil type” in more detail. Inthis case each foil is in the form of strips, such as 9 a, 9 b extendingperpendicularly to each other and terminating at one end in a pad 9 cthrough which fibre 5 a passes and is secured by the adhesive bead 6 aor solder contact if the fibre is metallised. FIG. 3 illustrates threedifferent arrangements, i.e. where the strips 9 a, 9 b join the pad 9 cat different locations (and in one case where strip 9 b is formedthrough two right angles before being joined to the pad. The other endsof the strips are attached to the fingers 2 c, 2 d of a comb likestructure of piezoelectric material. These fingers impart motion in eachof two respective orthogonal directions x-y (as shown) to the foilstrips, whereby the end portion of the respective fibre 5 a moves inthese directions, so that light emerging from the end faces 5 a′, 5 b′,5 c′ is deflected.

FIG. 4 is a cross-section, in elevation, (rotated through 90°), showinga set of optical fibres 5 passing through support structure 3, eachfibre being secured to respective foils 9, arranged in separated layers,in a foil stack (not shown in detail). Each of the foils is connected torespective fingers of a piezo electric comb structure 2 e, which ismounted in a support plate assembly 3 a in the support structure. Ribboncable 10 is connected to the piezo actuators to provide energization.

FIGS. 5 and 6 illustrate, more graphically, how the piezo electricmaterial comb structures 2 e are connected to the foil structures 9,which are attached to respective optic fibres 5, whereby the ends of theoptic fibres are caused to move in the focal plane of respective lenses12. FIGS. 5 and 6 show schematically a 4 port structure having only fourlenses, in order to simplify the drawing and explanation. The assemblycan, of course, have “n” lens elements for “n” fibres in an “n” portswitch, where “n” is the number of ports required in the particularapplication. The lenses 12 are supported in a block 13 which alsosupports capacitive position sensors (as explained below).

FIG. 7 shows four stages 7 a-7 d during the manufacture of a “monolithictype” of piezo electric material transducer. The first stage 7 aillustrates a body 7 of piezo electric material having a generallycylindrical shape. The second stage shows pairs of V-shaped saw cuts,V1, V2, V3, which form grooves defining a central pillar 14 oftriangular cross-section segments 15 a, 15 b, 15 c and peripheral thinpillars 16 a, 16 b, 16 c, each of triangular cross-section. Thesegrooves are then filled with a low-melting point alloy 17 in stage 7 c.Finally, further saw cuts S are made as shown in FIG. 7 d in order todefine three interconnects in the form of isolated conductive pads 18 onthe triangular sides of the central pillar 14. These pads are isolatedalong the length of each side edge due to the gap 19 (of piezo electricmaterial) which is opened up by the respective saw cut S. Electricalinputs to each of these pads cause the central pillar 14 to bend and toflex the fibre optic. The plan view of FIG. 7 e shows the individualmotion “d” imparted by each pad 18 when energised. By suitableenergization of these pads, a resultant motion can be achieved formoving the pillar 14 in the x-y axes. A through hole 20 bored in thebody of piezo electric material, along the longitudinal axis, receivesthe optic fibre as shown in the schematic diagram of FIG. 2.

A similar structure can be made by (a) moulding the pillar 14 ofpiezoelectric material prior to firing and (b) attaching the pads 18 bycoating. Such a pillar could be hollow or solid and of differentcross-sectional shapes.

FIG. 8 is a perspective view of a group of monolithic type transducers7. Each of these transducers supports a respective optic fibre 5, theterminal end of which moves in the focal plane of the respective lens12. This shows the fibre array in a hexagonal/triangular arrangement,but square arrays can also be used.

FIG. 9 is a cross-section through three monolithic transducers 7, eachmounted on a base board 3 which supports optic fibres 5. These are shownas having cladding 19 on the lefthand side of the board 3 and as fibresextending through transducers 7 which terminate in ends 7 a close toeach collimating plano-convex lens 12 of a lens array. A bi-convex lensarray can also be used. This separation is indicated by the gap 21,which is arranged so that light emerging from the end of each fibre isat the focal plane of the respective lens. Connectors 20 having bondwires connected to transducers 7 are also shown.

FIG. 10 is a schematic view of an assembly used in calibration duringsetting up. It shows beams of light 22 output from each of the lenses 12which first pass through (e.g.) a partially reflective mirror (e.g.dielectric multilayer stack or half silvered) 29, which partiallytransmits beams to a CCD device 23 and partially reflects the beams. Theposition of the straight through beams on the surface of the CCD 23 canbe related to the absence (or presence) of signals used to energise thepiezoelectric transducers. Likewise, the position of a deflected beamfrom a transmitter fibre, which is partially reflected by the mirror 29onto a receiver fibre (in the same stack), as well as partially incidenton the surface of the CCD 23, can be related to instantaneous signalsused to energise the piezoelectric transducers to cause differentdeflections. This enables the transducer drive signals to be derived forcorrectly aiming and steering the end portions of the fibres so that theoutput beams arrive at their correct destinations (i.e. the selectedreceiving fibres in the working switch). For example, lookup tables canbe used to remember the ideal fibre-tip positions at each end in orderto create required fibre-to-fibre couplings (i.e. cross-connectionsbetween transmitter and receiver ports. This enables operation of theassembly as a switch and the assembly would be made reversible (i.e. thetransmitter fibres can be the receiver fibres and vice versa).

FIG. 11 shows a different arrangement which can be similarly calibratedbut also used in operation, and where the beams of light 22 leaving thetransmitting collimating lens assembly 12 t are received by a receivinglens assembly 12 r, which focuses the light on respective optic fibres 5in a (similar) monolithic structure. The energising signals can besimilarly calibrated with regard to beams of light passing straightthrough, and being deflected, since the transmitting beams will bereceived by respectively different fibres. This arrangement is fully“reversible”, since the “transmitters” can be the “receivers”, and viceversa.

Referring to FIG. 11 a, it is to be noted that:

-   -   i. Each fibre in the switch is associated with a small        collimating lens    -   ii. Fibre tips are placed in the focal plane of each lens    -   iii. A collimated Gaussian beam will be produced if a fibre is        lit since light will emerge from the fibre tip in the focal        plane and be collected and collimated by the lens    -   iv. Movement of each fibre-tip within the focal plane results in        an effective angular swing of the collimated beam    -   v. By symmetry, any collimated beams which arrive at a target        lens will focus to a point in the focal plane of the target lens    -   vi. If a fibre-tip were placed at the point defined in (v) then        light will be coupled into the fibre

A combination of (iii) and (vi) permits fibre to fibre coupling. Lightfrom one fibre can be transformed into a directional collimated beam by(iii). By moving a lit fibre-tip (the “source”) it can be arranged thatthe collimated beam from its associated lens is directed as the lensassociated with a totally different fibre (the “target”). By moving thetarget fibre it can be arranged that light from the incoming collimatedbeam may be collected and thus a fibre-to-fibre coupling condition hasbeen set up. Since the optical system is symmetrical, the terms “source”and “target” fibre-tips can be used interchangeably and in a coupledscenario light can be transmitted in either direction.

Calibration would be carried out using the following steps:

-   1. Each fibre is ground in 2D and for each fibre the capacitance    values for retro reflection are located-   2. Sequentially each fibre is moved to the positions on the CCD,    using the retro reflection to calibrate the reference points.-   3. For each fibre to each fibre the 2x and 2y average voltages are    optimised for maximum coupling-   4. With 128 fibres (64 at each end) we have 64 x/y capacitance    values stored, i.e. 16,384 numbers. These are stored in the non    volatile memory of the switch and used as the target capacitance    values for the desired switch settings.

These steps refer to either the reflective or other straight-throughdesign.

Referring to FIG. 11 b, there exists an optimum rest position offibre-tips which confers important system benefits (including optimumcoupling efficiency).

With no effective deflection (i.e. no applied voltage on the piezoactuators), the collimated beam from each fibre tip should ideally aimtowards the centre of the target lens array (or, by reflection, to thecentre of the source array in a folded system). The aim of this is tominimise the bipolar fibre-tip translation required (from the restposition) to approximately one half of the array size.

Fibre tip Z positions must be within the depth of focus of the lensarray to ensure high quality collimated beams. All fibre tips must bewithin a range behind the back surface of the lens array glasssubstrate, defined by the focal length of the lens array.

The angle of fibres relative to the lens array should be ideally 90°.Any significant deviation from a perpendicular geometry may have adetrimental effect on coupling efficiency and limit scalability.

In order to sense the position of each individual optical fibre, foiltype or monolithic type (for correlating deflection with transducerdrive signals), capacitive coupling is employed between (e.g.) eachmoving end portion of the fibre optic (which is coated with conductingmaterial to form a moving plate), and other relatively fixed plates. Anarray of such coated fibre optics can be aligned inside a similar arrayof capacitive sensor pickup units. The array may be either square orhexagonal to ensure optimum packing density. Array sizes are scalable tolarger number of fibres (>1000) suitable for future high port countoptical cross connects for fibre optic communication applications.

The position of the optical fibre is determined by a measure of thecapacitive coupling between the fibre and capacitive sensor plates. Ascapacitive feedback determines the fibre optic position with respect tothe lens array 12, the capacitive feedback mounting unit is rigidlyconnected to the lens array to ensure precise reference to the fibres tothe lens centres. (An alternative embodiment uses fixed fibres and amoving lens). The capacitive sensor plate pickup units can be formedeither as shown in FIG. 12 or in FIGS. 13 a and 13 b.

FIG. 12 shows, in plan view, one method, where the sensor pickup unitformed from through-hole plated holes in an insulating board material30. The insulating board material may be printed circuit board or somealternative insulating material such as ceramic. The sensor holes aresegmented into four isolated quadrants designed “North”, “South”, “East”and “West” (N, S, E & W). Electrical contact is made to these withappropriate patterned electrical tracks 31N, 31S, 31W, 31E. Each(coated) optical fibre passes down the centre of the sensor hole.

FIGS. 13 a and 13 b show, in sectional view, an alternative arrangementin which the N, S, E and W capacitive sensor plates are formed byperpendicular arrays of parallel conductive tracks 31N, 31S, 31W, 31Eintersecting an array of holes through which the optical fibres 5 pass.The capacitive sensor tracks for NS and EW detection are arranged inparallel arrays, the two parallel arrays being perpendicular to eachother. For isolation, the NS & EW sensor arrays are isolated from eachother by sandwich layers of insulating matrix material 33. Ground planelayers 32 above and below each sensor layers act as a screen againstenvironmental electromagnetic pickup. Note that FIGS. 13 a and 13 b showonly two layers of NS and EW sensor tracks. Improved capacitive feedbacksensitivity may be achieved by increasing the number of sensor tracks(layers).

The arrangement of FIG. 12 results in a larger capacitive couplingbetween the fibre 5 and the sensor plates, whereas that of FIGS. 13 aand 13 b is inherently easier to manufacture (but to achieve sufficientcapacitive coupling between the NS and EW sensor tracks, a verticalarray of such tracks are required).

An AC voltage is applied to the conductive coating on each opticalfibre, typically at audio frequency. The resultant ac voltage coupled tothe sensor plates is then detected using an appropriate low noiseamplifier circuit, such as that shown in FIG. 14 (where similarcomponents are identified by similar reference numerals). The ac voltagegenerated on the sensor plates is proportional to the capacitivecoupling between the sensor plate and the fibre conductive coating. Thisdepends on the local distance of the fibre to the sensor plate.Combining information from 31N, 31S, 31E and 31W plates therefore givesinformation on the localised position of the fibre.

Increased positional accuracy is achieved by coupling the detectedvoltages on the N and S sensor plates to the two inputs of adifferential low noise amplifier 35. Thus as the optical fibre movescloser to the N plate, the N plate detected signal increases, similarlythe detected signal on the S plate decreases. The differential isapplied to the amplifier. A similar arrangement is used for the E-Wplates.

To enable the unique positions of individual fibres within large arraysof optical fibres to be detected, an AC signal needs to be applied toeach fibre. Such an arrangement is not practicable with large numbers offibres. We therefore prefer to use a method by which the uniquepositions of arrays of fibres may be detected by selectively switchingbetween diagonal rows of such fibres. Details are shown in FIG. 15. Bysequentially applying AC to the diagonal rows and by sequentiallyreading capacitive feedback signals from horizontal rows and columnsunique addressing can be achieved. This will now be described in moredetail below. (This diagonal switching can be used independently, i.e.in other switching assemblies.)

An AC excitation signal is applied to diagonal arrays of fibres (asshown in FIG. 15). For a 64 fibre switch array, there are 15 suchdiagonals, but by using a vertical and horizontal array of capacitivefeedback sensor tracks, arranged orthogonally, the number of addressablediagonals is reduced to just 8. This is explained with reference to FIG.15, which shows a 64 element array, but the following analysis isapplicable to any scalable array. In FIG. 15, the diagonals are A, B, C,D, E, F, G and H. Horizontal rows 0, 1, 2, 3, 4, 5, 6 and 7 such that,for example, the third fibre down from the top and the fifth from theleft is designated C2.

Diagonal array A utilises all 8 fibres along the diagonal. However,diagonal array B utilises 7 such fibres (B0 to B6), this diagonal istherefore connected to fibre B7 (bottom left corner). Similarly diagonalC comprises six such fibre elements (C0 to C5) and this is connected tofibre elements C6 and C7. The process is repeated so that all diagonalscomprise 8 elements. (However, this connection system can be scaled toany size of array). For example, a 256 fibre array comprising 16 rowsand 16 columns would be connected using 16 diagonals. A generalised Nfibre array therefore contains square root (N) diagonals.

Referring to the 64 fibre array shown in FIG. 15, the 8 rows and 8columns of the orthogonal capacitor sensing tracks are each connected to8 parallel differential amplifier detection circuits, such thatcapacitants is sensed along all rows and columns simultaneously; 1detection circuit per row and 1 detection circuit per column. Thecapacitor tracks need not be orthogonal, alternative angles can be usedas long as the tracks cross. As the excitation signal is applied alongthe diagonal and to only one diagonal at a time, only one unique elementin a row or column generates a capacitive feedback signal when detectedby the capacitive feedback circuitry. Thus for the present case of 64elements, for each diagonal excitation, 8 capacitive feedback signalsare read in parallel from each row and column. The outputs are connectedto an 8 channel ADC unit, one for the rows and one for the columns.

Note also that for very large arrays, the time to sense all elementswith the capacitive feedback system is limited by the time taken toexcite and scan each diagonal. Improved switching time can be achievedby sub-dividing larger fibre arrays into sub-sections, where, forexample, a 256 element array can be split into 4 smaller separatereadout arrays. This approach is scalable to any array size.

In order to provide a further improvement, a collimating lens can beattached to or integral with the end of the optical fibre to provide awider angular spread of the emergent beam. In this case, both the lensand fibre move together which simplifies the design enabling rapidswitching speed for a high port count. These collimating lenses can beused independently i.e. with other switching assemblies, but they areespecially useful when used together with the miniaturised “foil type”or “monolithic type” of piezo electric material transducers describedabove.

As the fibre end and lens array can both result in back reflection (evenwhen all faces are coated with multi-layer dielectric anti-reflectioncoatings), some signal loss is incurred. Furthermore, couplingefficiency between fibre ends and collimating optics is criticallydependent on maintaining the position of the fibre end within the focalplane of the lens. Collimated fibre optics can be used to deal with thisproblem. Insertion losses and back reflection within optical switchsystems can be considerably reduced and construction can be simplifiedby the use of collimated or integrally lensed fibre optic ends (FIGS. 16a and 16 b) in place of fibre optic ends and lens arrays.

Collimated fibre optics 40 are commercially available, they incorporatea collimating lens 40 a attached to the single mode fibre optic endportion 5.

Integrally lensed 41 fibre optics may also be used in place of acollimator 40 for all of the present applications discussed here.Integrally lensed fibre optics are formed by treating the fibre opticend in such a way that it forms a micro lens (integral lens fibre opticsystems are currently available from some manufacturers of fibre opticsystems). The advantage that both of these technologies provide in thepresent switching application is that the light emanating from the fibreoptic end is collimated and parallel without the incorporation ofadditional discrete optical components such as lens arrays.

Integrally lensed fibre optics may also be made by cementing anappropriate lens to the fibre end. In all cases coated or uncoatedcomponents may be used. Collimator based N×N fibre switches (i.e. Ninput port counts and N output port counts) have the advantage of lowinsertion loss, excellent cross talk performance, and excellentpolarisation independence.

Alternatively, fibre optic switching can be achieved in which collimatedor integrally based fibre optic ends are incorporated into the N×Nswitching matrix, thereby precluding the lens array 12 used in thealternative switch structures described above.

Where capacitive feedback is used (as described above) to determine theposition of the collimator, the external surface of the collimator ismetallised or given a conductive thin film coating.

Connection to the collimator can be made using metallised fibres andcapacitive feedback can be used to measure the capacitance between theouter surface of the collimator rather than the metallised fibre optic.However, if integrally lensed optics are used, capacitive coupling isused to measure the capacitance between the sensor pcb and themetallised fibre.

FIG. 17 shows schematically how the collimated or integral lens on thefibre optic end can be incorporated into a monolithic piezo fibre opticswitch. This is one simplified solution in which the lens array 12 isreplaced by the collimator 40 or integral lens 41. Although not shown inFIG. 17, it is possible that the length of fibre between the top of themonolithic piezo actuator and the collimator may be increased.

To achieve greater angular swing of the collimated optics at the end ofthe fibre optic it may be mounted in a gimbals type mount 42 that allowsthe collator 40 to pivot about its centre point as shown in FIGS. 18-20,to provide movement in x-y axes 43. A flexure joint is preferably usedwhich links the collimator to the extension arm of the piezo actuator asshown, for example, in FIGS. 19 and 21. Both gimbals and flexure jointsmay be manufactured by a variety of means including patterned foil. FIG.21 shows how the use of foils coupled with a gimbals arrangement may beused to tilt the collimated or integral lens fibre optic end. In thiscase the gimbals arrangement may also be made using a patterned foilstructure.

FIG. 19 and FIG. 20 show a variant of the collimator mounting scheme inwhich a tapered piece 44 forms an extension of the piezo tube 8. Theextension piece 44 provides mechanical advantage, i.e. it providesgreater XY movement of the collimator base than that generated by thepiezo tube scanner alone. The extension piece therefore gives mechanicaladvantage to the piezo actuator movement. (The exit beam is shown as 45in FIG. 19). The piezo actuator extension rod 44 is tapered to reducethe resonant frequency of the mechanical system.

A key feature of this design is that the extension rod 44 provides extralateral movement in the XY plane (perpendicular to the fibre axis) ofthe base of the collimator than that provided by an unextended piezoactuator alone. The advantage of this is that the collimated beam may beswung over a large, angular range for a given piezo movement. This isimportant as it provides a much wider addressable range for theresulting beam emanating from the collimator, thus enabling much largerswitch arrays to be built (i.e. larger N×N switch sizes—higher portcounts).

With the monolithic type, the optical fibre passes through the centre ofthe piezo tube scanner. The complete unit is replicated N times for anN×N switch unit (FIG. 22)—note FIG. 22 shows only the piezoactuators—where the array may be either square or hexagonal/triangularin layout.

Individual piezo actuators are formed by moulding, firing and/orsubsequent sawing of the monolithic piezo material, followed bypatterning with electrical contacts.

FIG. 20 shows (in exaggerated schematic form), displacement of the fibreactuator assembly. The fibre optic is not shown in this drawing—itpasses through the centre of the piezo tube actuator 8.

The collimator gimbals and flexure mount could be manufactured in anumber of ways, one route being patterned foils. FIG. 21 shows onepossible method of manufacture for the gimbals mount. Alternatively ameander type foil arrangement may be used to manufacture the flexuremount.

FIG. 23 shows an alternative embodiment of a monolithic type piezoelectric material actuator. In this case the fibre optic 5 (shown bentthrough a right angle) is held fixed in a mounting block 52 which alsosupports electronic interconnects and capacitive sensing plates(associated respectively with the fixed fibre and the moving lens).These sense lens displacement and provide a feedback control signal (asdescribed above). The lens 50 is supported by a lens mount 51 which isconnected to a monolithic type piezo electric material actuator via aconnecting lever 53. The isometric view of FIG. 24 shows a clearancehole 54 which enables freedom of movement. FIG. 25 shows a plurality ofthese actuators mounted on a rigid support plate and PCB 55 forproviding drive connections. As shown in FIG. 23 a, for example, theextension rod 7 terminates in a tapered portion 53 and cylindricalrod-shaped portion 57 which is connected to lens mount 51. (see alsoFIG. 24). This arrangement is particularly advantageous becausecollimating lens 50 can have a conductive coating, to act as a capacitorplate and it is conveniently positioned with respect to the fixedmounting block 52, on which can be provided another capacitor plate(e.g. in confronting relationship), to provide positional feedbackinformation as a result of capacitive changes. Moreover, thisarrangement allows the components to be conveniently located on acapacitive sensing support structure, of laminar form, like thatdescribed with reference to FIGS. 13 a and 13 b. This will also be moreapparent from the sub-assemblies shown in FIGS. 29 and 31-34 where thecapacitive sensing system includes flat conductive tracks, which areassembled in a laminar form, in a support structure or block, which canconveniently support other components of the switching assembly. Thisprovides both the advantages of capacitive sensing with a compact androbust structure which facilitates manufacture.

FIGS. 26 a-26 e are plan views of an example of foil designs for a 64port foil type switching assembly. These are arranged in layers,insulated from one another, in the sub-assembly of optic fibre bundles.

FIG. 27 is a perspective view of a piezo electric comb structure 2, fora foil type design of switch, showing saw-cuts 60 separating individualactuators 1 and also showing metallised contacts 61, 62, 63. FIG. 27 ashows how the fingers of the comb structure 2 are attached to respectiveconductive tracks of a flat flexible connector 2′. The piezo combincludes outer layers forming respective common +V and −V planes and aninner layer forming a control V plane.

Referring to FIG. 27 b, this schematically illustrates preferredbias-drive for enhancing the lifetime performance of the piezos. Thisessentially involves never driving either half of piezo bimorphs in sucha manner that they could otherwise be depoled. Bias-driving thusincreases device longevity. Another advantage is that the number ofelectrical interconnects to piezo combs can be drastically reduced.Essentially the top electrodes for all elements of the comb are madecommon, the bottom electrodes for all elements of the comb are also madecommon and only centre electrodes of the elements need independentcontrol. Thus, for a comb of 8 bimorphs, there are only 8+2 (10)electrical interconnects, rather than 8+8+8 (24).

FIGS. 28 a-28 e show plan views of each layer of piezo-comb arrays andfoil arrangements such as those shown in FIGS. 26 a-26 e. These areassembled into a switching assembly as shown in FIGS. 29 and 30. FIG. 29shows a 5 foil stack 64, piezo combs 2 in a support plate 65 to whichelectrical connections are made by ribbon cable 66, the components beingmounted in a support structure 67. An optic fibre array 5 passescentrally through structure 67, as shown also in the rear view of FIG.30.

FIGS. 31 a and 31 b are cut-away perspective views of a monolithic typeof switching array in which monolithic tube type piezo actuators 70deflect metallised fibre optics 71 that terminate in (or adjacent)collimators 72 mounted in a capacitive sensing feedback board 73;mechanical leverage (like that shown in FIG. 20) being applied by theextension levers 74 (an enlarged view being shown in FIG. 31 c).

FIGS. 32 and 33 show foil type sub-assemblies in a later stage ofcompletion, and FIG. 34 shows two of the sub-assemblies facing eachother across a space in which the beams are projected.

APPENDIX A

An example of a method of making a monolithic type of piezoelectrictransducer is described in more detail below, all electrical connectionsfor steering the fibres are brought out to bonds pads on the edge of theceramic and three connections each are supplied with voltages to drivethem.First step: Interconnects are laid out on ceramic base. Two layermetalisation, out to the array of bond pads around edge.Second step: A coarse pattern low temperature ceramic screen is printedand fired.Third step: Holes in the pattern are plated up, connecting tointerconnects beneath.Fourth step: A piezo slab, of grade used for inkjet print heads orequivalent, suitable for diamond sawing bonded to ceramic base using lowmelting point alloy.Fifth step: Holes drilled through (to clear fibre core)Sixth step: First hexagonal saw, cut step (FIG. 7)Seventh step: The sides of the columns are plated or deep evaporated.Fibre holes also plated or evaporated, as well as back side of ceramicfor use as earth connection to fibre holes. Tops of columnsdemetallissed if needed.Eighth step: Piezo poled under oil, producing radial poling in columns.Ninth step: Second second of hexagonal sawing, produces final columns(FIG. 7). Need further cut to reduce metal thickness if plated ratherthan evaporated. Wire bond or solder pads to electrical connectors.Fibre cores are dropped through (ends already prepared) with devicejigged up above flat and locating grid. Drop in UV cure epoxy to eachfibre and expose.Eleventh step: Attach and focus microlens arraysTwelfth step: Assemble back to back with matching array or mirror.Attach fibre tails to connectors.Number of fibres accessible in hexagonal array given fiber can bend ntimes the spot separation from the centre point is n(n=1)3+1. i.e. adeflection capable of +/−10 spot sizes gives access to 334 spots—1334×334 nonblocking switch. To realise this performance, the correctpath length needs to be used.The quality of the lens array is important in achieving diffractionlimited gausian beams needed to maximise performance. Given a highnumerical aperture and small field of view used, a single surfaceparabolic form produces excellent results, built up of multi layerdeposited silica and then reflowed.Response time is set by the frequency of the columns plus fibre. Theshorter and fatter the better (this is an opposite requirement tomaximising displacement). Having column getting lighter toward top isgood.Deflection is achieved using this radial poled system radial poled andvolts applied between three sides and the centre. Using shear modedeflection avoids need for repoling (can use prepoled throughthickness), but gives much lower deflection. Maximum deflection obtainedwith multilayer stack poled through thickness, but this needs severallayers.Aid to alignment can be had in the single pack against mirrorconfiguration by using a partially transmissive mirror, and a CCD in theplace where the other fibre pack would go. This can be used on line ifdesired in this configuration, or simply as a set up for the electronicsto learn the right drive voltages for all locations of all fibres.

1. An optical fibre switching assembly, comprising: (a) a first set ofoptical components incorporating a number of optical guides spaced froma second set of optical components incorporating a number of opticalguides; (b) collimating means corresponding to each optical guide; (c)actuating means which flex when actuated and are operatively connectedto said collimating means for individually moving said collimatingmeans; and (d) means for controlling the actuating means so that opticalradiation is transmitted from a selected guide in the first set andreceived by a selected guide in the second set.
 2. An assembly accordingto claim 1, wherein the collimating means has first and secondextremities, the actuating means have means which engage the firstextremity of the collimator, the collimating means being constrained sothat when the actuating means for moving said collimating means displacein one direction said second extremity displaces in essentially theopposite direction.
 3. An assembly according to claim 1, wherein theassembly has a support structure and the collimating means arerespectively mounted to said support structure through a mount forconstraining the collimating means so that the collimating meansdisplaces in a rocking movement when moved by the actuating means.
 4. Anassembly according to claim 1 in which, said means for moving thecollimating means incorporates a monolithic transducer which cooperateswith mechanical leverage means to magnify the transducer movement.
 5. Anassembly according to claim 4, in which the leverage means includes agimbal mounting, a flexure mounting, and an extension rod locatedbetween one end of the body of the transducer and a mounting point onthe gimbal spaced from its pivotal axis.
 6. An assembly according toclaim 1, wherein said collimating means includes at least one lensintegral with, or fixed to the end of said guide, whereby the guide andthe lens move together.
 7. An assembly according to claim 1, in whichthe actuating means for moving the collimating means includeselectrostatic means.
 8. An assembly according to claim 1, in which theactuating means for moving the collimating means includes a piezoelectric transducer means.
 9. An assembly according to claim 8, wherethe piezo electric transducer means is of a “monolithic type”, wheresaid transducer is made of piezo electric material, has a body with alongitudinal axis, and the body has conductive strips aligned with alongitudinal axis so as to define respective portions of the transducerthat impart respective transverse motions in different radial directionsto provide a resultant motion in the two dimensional plane perpendicularto the longitudinal axis.
 10. An assembly according to claim 8, in whichthe piezo electric transducer means is of a “foil type”, where fingersof a comb-like array of piezo transducers are attached to actuatingmembers, such as foil strips, for producing orthogonal displacement ofone of the optical guide and the collimating means, whereby the foilsand combs can be assembled in a laminar matrix.
 11. An assemblyaccording to claim 1, wherein position sensing means are provided tosense the position of at least one of the assembly components which aremoved by the actuating means, whereby the optical radiation istransmitted from first to second set of collimating means without anyintermediary position sensing means.
 12. An assembly according to claim11, further comprising a control system, wherein said position sensingmeans operate with position sensing feedback means whereby the positionsensing feedback means feed at least one feedback signal representativeof the amount of deflection of said moved assembly components to saidcontrol system and said signal is used by the control system to ensurethat any of said collimating means of the first set is aimed at anyselected collimating means of the second set.
 13. An assembly accordingto claim 11, wherein the position sensing means sense capacitive changesto determine a position; at least one of said guides having a conductivecoating acting as at least one capacitor plate which moves with respectto at least one other fixed capacitor plate, thereby giving positionalinformation of at least one of the guides and the collimating means. 14.An assembly according to claim 11, wherein the position sensing meanssense capacitive changes to determine a position, at least one of saidcollimating means having a conductive coating acting as at least onecapacitive plate and operating in conjunction with at least one othercapacitive plate which is part of an adjacent supporting structure. 15.An assembly according to claim 11, wherein the position sensing meansincludes conductive tracks, crossing at points where pairs of conductivetracks, associated with one of individual guides and collimating means,are adapted to detect capacitive changes.
 16. An assembly according toclaim 11, wherein the position sensing means uses a diagonal addressingsystem, wherein a signal is applied sequentially to diagonals of sensedpoints, and capacitive changes are read sequentially from each row andcolumn.